Low Temperature Co-Fired Ceramic (LTCC) Tape Compositions, Light-Emitting Diode (LED) Modules, Lighting Devices and Methods of Forming Thereof

ABSTRACT

The present invention provides LTCC (low temperature co-fired ceramic) tape compositions and demonstrates the use of said LTCC tape(s) in the formation of Light-Emitting Diode (LED) chip carriers and modules for various lighting applications. The present invention also provides for the use of (LTCC) tape and LED modules in the formation of lighting devices including, but not limited to, LED devices, High Brightness (HB) LED backlights, display-related light sources, automotive lighting, decorative lighting, signage and advertisement lighting, and information display lighting.

FIELD OF INVENTION

This is a divisional application of U.S. Ser. No. 11/510,170 filed onAug. 25, 2006. This invention is related to LTCC (low temperatureco-fired ceramic) tape compositions and the use of said LTCC tape in theformation of Light Emitting Diode (LED) chip carriers and modules forvarious lighting applications including, but not limited to, LEDbacklights, Liquid Crystal Display (LCD) lighting, display-related lightsources, automotive lighting, decorative lighting, signage andadvertisement lighting, and information display applications.

TECHNICAL BACKGROUND OF THE INVENTION

Solid state electronic devices can be fabricated with conjugated organicpolymer layers. Conjugated polymer-based diodes and particularly lightemitting diodes (LEDs) and light-detecting diodes are especiallyattractive due to their potential for use in display and sensortechnology. This class of devices has a structure that includes a layeror film of an electrophotoactive conjugated organic polymer bounded onopposite sides by electrodes (anode and cathode) and carried on a solidsubstrate.

Generally, materials for use as active layers in polymer diodes andparticularly PLEDs include semiconducting conjugated polymers thatexhibit photoluminescence. In certain preferred settings, the polymersexhibit photoluminescence and are soluble and processible from solutioninto uniform thin films.

The anodes of these organic polymer-based electronic devices areconventionally constructed of a relatively high work function metal.This anode serves to inject holes into the otherwise filled p-band ofthe semiconducting, luminescent polymer.

Relatively low work function metals, such as barium or calcium, arepreferred as the cathode material in many structures. This low workfunction cathode serves to inject electrons into the otherwise emptyp*-band of the semiconducting, luminescent polymer. The holes injectedat the anode and the electrons injected at the cathode recombineradiatively within the active layer and light is emitted.

LED lighting can commonly be characterized by on-axis luminous intensityexpressed in candela. Intensity describes the flux per solid angleradiated from a source of finite area. Furthermore, flux is the totalamount of light emitted from a source in all directions. For the purposeof this invention, flux will be used to describe the brightness of LEDs.

Radiometric light is specified according to its radiant energy and powerwithout regard for the visual effects of the radiation. Photometriclight is specified in terms of human visible response according to theCIE standard observer response curve. Furthermore, in the fields ofphotonics and solid state physics, luminous efficacy is defined as theconversion between photometric flux, expressed in lumens, andradiometric flux, expressed in watts.

It is noted that the luminous efficacy is a function of the dominantwavelength of a specific LED lighting source. For example, an IndiumGallium Nitride (InGaN) LED shows increasing luminous efficacy from 85to 600 lumens per watt corresponding to a shifting of the dominantwavelength from 470 to 560 nm. On the other hand, an Aluminum IndiumGallium Phosphide (AlInGaP) shows decreasing luminous efficacy from 580to 800 lumens per watt corresponding to a shifting of the dominantwavelength from 580 to 640 nm. For the purpose of this invention,luminous efficacy at the peak transmittance of LED is referred.

Most typical prior art LEDs are designed to operate no more than 30-60milliwatts of electrical power. More recently, commercial LEDs capableof continuous use at one watt of input power were introduced. These LEDsuse much larger semiconductor chips than previous LEDs to handle thelarge power. In order to dissipate heat to minimize junction temperatureand maintain lighting performance, these larger chips are normallymounted to a more effective thermal conductor (such as metal slugs) thanprevious LED structures.

Typically, the 5-watt LEDs are available with efficacy of 18-22 lumensper watt, the 10-watt LEDs are available with efficacy of 60 lumens perwatt. These 10-watt LED light devices will produce about as much lightas a common 50-watt incandescent bulb and will facilitate use of LEDsfor general illumination needs.

Despite the prior art LED devices currently available, a need stillexists for improved LED modules which can provide improved performancecharacteristics, such as increased heat dissipation qualities, improvedmanufacturing processes, and lower cost benefits. Other benefits includecloser TCE match to the chip, smaller size, light weight, environmentalstability, increased circuit integration capability, enhanced lightreflectivity, simplified fabrication (such as co-fireability of amultilayer structure), higher yield, broader process tolerance, highmechanical strength, and effective heat dissipation. None of the priorart LEDs provide for the use of LTCC technology or the benefitsassociated with the incorporation of LTCC technology, which includelonger device life.

Various design and configuration of the HB (High Brightness) LED chipcarrier devices were provided in the prior art. However, they allpresented different problems related to various functions,manufacturability, and cost. Functioning LED devices with equal orgreater than 0.5 Watt and preferably 1 Watt power rating are stillneeded for lighting applications, including HB LED modules for LCDapplications, which allow for the improvement in heat dissipationproperties to improve the overall color quality of emitting light diodemodules and increase the module life. The present invention has providedsuch materials, methods, chip carriers, and modules to allow for such aninnovation in lighting technology.

SUMMARY OF THE INVENTION

The present invention provides a light emitting diode chip carrier and amethod of forming a light emitting diode chip carrier comprising: (a)providing two or more LTCC tape layers; (b) forming one or more cavitiesin said tape layers; and (c) providing at least two electrical vias andat least one thermal via in said tape layers; and wherein said LTCC tapelayers provide a desired circuit pattern and said circuit pattern iselectrically connected through said electrical vias, thus, forming afunctioning chip carrier.

The present invention further provides a light emitting diode and methodof forming a light emitting diode module comprising: providing two ormore LTCC tape layers; forming one or more cavities in said tape layers;providing at least two electrical vias and at least one thermal via insaid tape layers; providing at least one functioning light emittingdiode chip; wherein said LTCC tape layers provide a desired circuitpattern and said circuit pattern is electrically connected through saidelectrical vias, thus, forming a functioning chip carrier and wherein atleast one functioning light emitting diode chip is mounted to said chipcarrier. Additionally, the light emitting diode module is disclosedwherein at least one thermal via is connected to a heat sink and whereinsaid thermal via dissipates heat released from said functioning lightemitting diode chip through its connection to said heat sink.

In one preferred embodiment, the LTCC tape is a “white” tape used in theformation of a LED module for use as a HB LED backlight.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 provides schematic diagrams of chip carrier design with wirebonding.

FIG. 2 represents a schematic diagram of the chip carrier design withwire bonding and solder attachment.

FIG. 3 provides a schematic diagram of the chip carrier design with LEDflip chip attachment.

FIG. 4 provides a schematic diagram of the LED placement at the cavityof the chip carrier.

FIG. 5 provides a schematic diagram of the chip carrier with LED flipchip attachment and thermal vias.

FIG. 6 details placement of four LED chips at the cavity of the chipcarrier.

FIG. 7 details a typical prior art LCD structure.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides LTCC (low temperature co-fired ceramic)tape compositions and demonstrates the use of said LTCC tape(s) in theformation of Light-Emitting Diode (LED) chip carriers and modules forvarious lighting applications. The present invention also provides forthe use of LTCC tape and LED modules in the formation of lightingdevices including, but not limited to, LED devices, HB LED backlights,display-related light sources, automotive lighting, decorative lighting,signage and advertisement lighting, and information display lighting.

This invention further relates to the material compositions andfabrication processes of chip carriers for HB LED backlight applicationswherein a co-fireable LTCC with built-in cavity provides the base tomount one (white, Red, Green, or Blue) or a multiplicity of at leastthree (Red, Green, and Blue) LED chips or at least four (a combinationamong white, Red, Green and Blue) LED chips. The said LTCC structurealso provides thermal vias which effectively dissipate the heat releasedfrom all functioning chips through their connections to heat sink (aheat sink can be a metal core printed circuit motherboard (MCPCB)). Thebonding to heat sink can be provided by braze, solder, or otherthermally conductive glue. Un-pigmented white color tape compositionswith a variety of white color ceramic fillers are to provide mechanicalstrength and light reflection suitable for the HB LED chip carrierpackage applications. In the cases where specific color enhancement isneeded, a variety of inorganic colored pigment is added to the tapecompositions to be used as the LTCC materials. A family of co-fireablesilver, copper, gold, silver/platinum, silver/palladium thick filmcompositions are to provide various functions including but not limitedto circuit connections, via fill connections, thermal vias, and lightreflection for the HB LED chip carrier package applications.

While the present invention is described by referring to HB LEDapplications, it is understood that various embodiments may be used in amultitude of lighting applications. The present invention furtherprovides for novel lighting devices including: (1) thin and lightweightmessage displays, such as public information signs at airports, trainstations, and other places; (2) status indicators, such as on/off lightson professional instruments and consumers audio/video equipment; (3)infrared LEDs in remote controls for TVs, DVDs, and VCRs; (4) clustersin traffic signals to replace ordinary light bulbs behind colored glass;(5) car indicator lights; (6) bicycle lighting; (7) calculator andmeasurement instrument displays; (8) red or yellow LEDs for indicatorand alpha numeric displays in environments where night vision must beretained, such as in aircraft cockpits, submarine and ship bridges,astronomy observatories, and in the fields such as night time animalwatching and military field use; (9) red or yellow LEDs in photographicdarkrooms to provide lighting which doesn't result in unwanted exposureof films; (10) illuminations such as flashlights or torches; (11)emergency or signaling beacons and strobes; (12) movement sensors formechanical and optical computer mice and trackballs; (13) high-end LEDprinters; and (14) general household illuminations.

Although some of the above applications can be derived by LEDs ofsmaller wattage and lower brightness, this invention provides the meansto use fewer LED lighting modules to provide equivalent or superiorlighting performance, while further simplifying the fabrication processand reducing the cost.

For the purpose of this invention, HB LED packages are referred to ashaving luminous efficacy of greater or equal to 15 lumens per wattwherein these LEDs are normally associated with a power rating of equalof greater than 0.5 watt with a preferred rating of equal or greaterthan 1 watt.

This invention discloses cost-effective and simplified fabricationmethods to provide a monolithic glass-ceramic chip carrier for one(white, Red, Green, or Blue) or a multiplicity of at least three (White,Red, Green, and Blue) LED chips with either a built-in circuit driver ora connection to an external circuit driver while providing passage waysfor heat dissipation.

It is noted that some specific combinations of LED chip and anyassociated optical materials are needed to provide white light from asingle chip set or module. For the purpose of this invention andthroughout the text and claims, “White LED chip” is used to representthese types of specific LED chip and optical material combinations, solong as they produce white light. For example, most white LEDs inproduction today use a 450-470 nm blue Gallium Nitride (GaN) LED coveredby a yellowish phosphor coating usually made of Cerium-doped yttriumAluminum garnet (YAG:Ce) crystals. The single crystal form of YAG:Ce isconsidered as a scintillator rather than a phosphor. Since yellow lightstimulates the red and green receptors of the human eyes, the resultingmix of blue and yellow light gives the appearance of white. White LEDscan also be made by coating near UV emitting LEDs with a mixture of highefficiency Europium based red and blue emitting phosphors plus greenemitting copper and aluminum doped zinc sulfide (ZnS:Cu,Al). Anotheroption to produce white light LEDs uses no phosphors and is based onhomoepitaxially grown Zinc Selenide (ZnSe) on a ZnSe substrate whichsimultaneously emits blue lights from its active region and yellow fromthe substrate. Although a white light is normally applied as a LCD(Liquid Crystal Display) backlight, regardless of whether the light iscoming from an aforementioned single chip set or a combination of Red,Green, and Blue LED's, the LTCC chip carrier package of this inventioncan also provide various colored light with its color enhancement anddurability contributed by and not limited to the use of various types ofinorganic pigments and an effective heat dissipation as discussedfurther in the text.

In this invention, the thermal vias directing the heat dissipation arebrazed to at least one heat sink making the assembly a single piece ofstructure which can provide the needed functions as a HB LED packagedevice. Furthermore, this invention provides a family of co-fireablesilver and copper thick film compositions which provide variousfunctions including but not limited to circuit connections, via fillconnections, thermal vias, and light reflection for the HB LED packageapplications.

FIGS. 1A through 1F are the schematic diagrams of chip carrier designwith wire bonding with the following details: FIG. 1A is across-sectional view of a chip carrier with wire bonding. The LTCC chipcarrier is shown with a cavity surround on four sides by top tier LTCCdielectric 111. One LED chip is mounted at the center of the cavity withthermal vias 106 resided in the second tier LTCC dielectric 108.Co-fireable conductor provides terminations 103 (top tier), 110 (secondtier), external termination 105 on motherboard 109, and heat spreader114. The chip is connected to the second tier termination by wirebonding 113, and further connected to the external termination by wirebonding 104. Termination 110 is connected to termination 103 by vias112. The chip is encapsulated in epoxy or other organic material 102.For further heat dissipation, a heat sink 107 is provided and variousmethods can be used to attach the heat sink to the opposite side ofcircuit board. FIG. 1B displays the terminations 103 which are used aspads for wire bonding. FIG. 1C displays the cavity 115 in the top tierof a multilayer LTCC dielectric 111, with the conductive vias shown as112. FIG. 1D displays the conductor layout at the bottom of the cavity;conductor patterns 110 at the left and right hand side serve as eithercathode or anode for chip connection whereas conductor pattern 116provides the bonding pad for the chip and its connection to the thermalvias. FIG. 1E displays the second tier of a multilayer LTCC dielectric108 with a typical arrangement of thermal vias 106. FIG. 1F displays aheat spreader 117 at the bottom of the thermal vias.

FIGS. 2A through 2E are the schematic diagrams of the chip carrierdesign with wire bonding and solder attachment with the followingdetails: FIG. 2A is a cross-sectional view of a chip carrier with wirebonding and soldering. A chip is mounted on the second tier 213 of themultilayer LTCC dielectric, wherein wire bonding 203 is used to connectthe chip to electrodes 205 (including both cathode and anode) which inturn are connected through conductive vias 206 and solder 207 to theexternal circuitry 208 deposited on a motherboard 209. Furthermore,thermal vias 212 underneath the chip are connected to a heat spreader211 which is brazed to a motherboard 209. It is noted that the brazejoint 210 can be substituted by solder joint or a connection made with aconductive adhesive. FIG. 2B displays the top tier of the multilayerLTCC dielectric 204 with a cavity 214. FIG. 2C displays both cathode205A and anode 205B at the left and right side, whereas conductorpattern 215 provides the bonding pad for the chip and its connection tothe thermal vias. FIG. 2D displays the second tier of a multilayer LTCCdielectric 213 with a typical arrangement of thermal vias 212. Twoconductive vias 206 are displayed to indicate the electrical connectionpath. FIG. 2E displays a heat spreader 211 at the bottom of the thermalvias 212 with via capture pads 216 which are soldered to the externalcircuit 208 on the motherboard.

FIGS. 3A through 3D are the schematic diagrams of the chip carrierdesign with LED flip chip attachment with the following details: FIG. 3Ais a cross-sectional view of chip carrier wherein a LED flip chip 301bonding is applied. A cavity is formed in the top tier of the multilayerLTCC dielectric 307 and electrode patterns are located on the surface ofthe cavity or in between the top tier 307 and the second tier 304 of themultilayer LTCC dielectric. Additional electrode patterns are located onthe bottom surface of the second tier wherein electrode 305 is connectedto the electrode 303 through the castellation via 309. FIG. 3B displaysthe top tier 307 of the multilayer LTCC dielectric with a square cavity308. FIG. 3C displays electrode patterns 310 and 311 representing anodeand cathode or vice versa. The connection is made by a conductive path303 and a castellation via 309. The location of chip mount is depictedwith a dash line border. FIG. 3D displays the back side of FIG. 3Cwherein four conductive patterns 305 are connected with castellationvias 309. Furthermore, a heat spreader 306 is patterned at the center.

FIG. 4 is a schematic diagram of the LED placement at the cavity of achip carrier wherein three LED chips, Red (R) 109, Green (G) 106, andBlue (B) 104 are placed on a thermal spreader pad 107 and connected to acommon cathode 105. The R, G, and B chips are further connected to theanodes, respectively, 111, 112, and 114. The respective connectingconductor patterns 110, 113, and 102 on this surface are connected tothe circuitry at other locations including different LTCC tape layer bycastellation vias 101.

FIGS. 5A through 5D are the schematic diagrams of a chip carrier withflip chip attachment and thermal vias with the following details: FIG.5A is a cross-sectional view of a chip carrier wherein a flip chip 501is bonded to a cathode 503 and an anode 511 electrode as shown in FIG.5B. The cavity is created in the top tier of the multilayer LTCCdielectric 502. The heat dissipation is provided by (1) the thermal vias504 in the second tier of the multilayer LTCC dielectric 509, (2) a heatspreader 505, (3) the thermal vias 506 in the third tier of themultilayer LTCC dielectric 508, and (4) a heat spreader 507. FIG. 5Bdisplays the second tier 509 of the multilayer LTCC dielectric whereinthe larger area conductive pattern presents a cathode 503 with an arrayof thermal vias 504. The anode 511 is connected to the externalcircuitry through a castellation via 510. The location of chip mount isdepicted with a dash line border at the center stage of 509. FIG. 5Cdisplays the third tier of the multilayer LTCC dielectric 508 with aheat spreader 505. An array of thermal vias 506 is also created for heatdissipation. Castellation vias 512 are also used to connect the anode tothe external circuitry. FIG. 5D displays the bottom side of the body 508wherein a central heat spreader 507 is used to connect the thermal viasto the heat sink by brazing wherein the conductive pads 513 are used tomake the connection to the motherboard.

FIG. 6 displays the placement of four LED chips at the cavity surface606 of a chip carrier. More specifically, two Green (G) 603 and 609, oneRed (R) 610, and one Blue (B) 604 LED chips are placed inside thehexagonal conductor layout. Both of the G chips are connected to thecommon anode 602, and cathode 608. The R chip is connected to anode 601and cathode 611. The B chip is connected to anode 605 and cathode 607. Acircular area depicted by the dashed line 612 represents the location ofcavity for LED chip mount.

To illustrate the application of this invention as an improved backlightunit on LCD, a description of LCD structure is provided herein. Adrawing of typical LCD stack is provided in FIG. 7A comprising six majorcomponents. These major components together with their respectiveelements located in sequence from the LCD viewing side are: (1) a frontpolarizer stack 701 comprising an anti-reflectance or anti-glare film, aviewing angle film, and a front polarizer; (2) a color filter 702comprising a front glass, a black matrix/color filter, a commonelectrode, and an alignment layer; (3) a liquid crystal layer 703; (4) aTFT, thin film transistor array 704 comprising an alignment layer, adisplay electrode, and a rear glass; (5) a rear polarizer stack 705comprising a rear polarizer, and a recirculating polarizer of DBEF, dualbrightness enhancement film; and (6) a backlight unit 706. The backlightunit 706, illustrate in FIG. 7B is further comprised of a front diffuser707, at least one layer of prism sheet of BEF, brightness enhancementfilm 708, a rear diffuser 709 and a lamp and light guide 710. A blackreflector is normally provided in 710 to enhance the brightness of thelamp.

The current invention provides a superior alternative to the lamp by theuse of a LED lighting module made with a LTCC chip carrier wherein atleast one HB LED chip is mounted and its circuit integration and heatdissipation are provided respectively by thick film conductor,electrical via, and thermal via materials. This provides the benefits ofstable and improved lighting performance, simplicity of fabrication ofbacklight units, reliability of lighting performance in the life of LCD,and overall cost.

Although the above description constitutes an embodiment of LED lightingmodule for LCD backlight application, it is noted that the saidapplication is not limited to LCD. White or colored LED lightapplications can be easily performed by those skilled in the art withthe current invention. It is understood that the LED module of thepresent invention may comprise red, green, blue, white, yellow or otherpigment colors, depending upon the anticipated application. Severalexamples are given below.

Two material and technology groups, LTCC glass-ceramic dielectric tapecompositions and thick film conductor compositions, are essential torealize this invention. Therefore, the two following sections aredevoted to provide detailed descriptions of the LTCC dielectric tapecompositions and thick film conductor compositions of this invention.

LTCC Glass-Ceramic Dielectric Tape Composition(s)

The tape composition(s) of the present invention comprise glass, ceramicfiller, and in a preferred embodiment, inorganic pigment. In oneembodiment, the tape composition comprises at least one glass frit, atleast one white color refractory inorganic oxide, and/or other inorganicpigment, which provides the white color enhancement and/or reflection.It is noted that, if advantageous, a variety of inorganic coloredpigment can be used at 0-10 weight % in the total inorganic substancesto provide specific color such as Red, Green, or Blue for display colorenhancement by the LED chip carrier.

Depending on the preferred color, the weight % content of inorganicpigment may vary. For example, 0.5% (weight percent based on totalinorganic materials) of cobalt aluminate can be added in a glass-ceramicwith a aluminum oxide refractory filler to provide a sintered ceramicbody of blue color. However, it is necessary to use 1.5 to 2.5% of ablack pigment, copper chromite spinel, ShepherdColor's 20C980 to show asufficiently black color. For the purpose of this invention, for almostall of the colors except black, a predetermined color of the LTCC chipcarrier can normally be provided with 0.1 to 10.0 weight % of thecorresponding pigment in a ceramic slurry composition comprising fritand refractory filler such as aluminum oxide, and preferably with 0.5 to1.0% of a given inorganic pigment in the first embodiment. Higher weight% content of pigment normally provide stronger color, but, the optimumweight % of the pigment content depends on the intrinsic properties ofthe chosen frit since it should provide proper softening and adequateflow during the process of densification or sintering. Furthermore, anoptimum composition including the weight % content of a given inorganicpigment depends on the wetting power of a given molten frit on thesurface of a given inorganic pigment, the ability to form a crystallinephase, particle sizes and surface reactivity of the inorganicingredients, among other factors. To achieve darker color, the secondembodiment of the slurry composition requires a higher weight % contentof a given inorganic pigment, such as from 1 to 10 weight % preferablyin the range of 1 to 4 weight %. One other critical property to considerwhen optimizing the ceramic slurry composition is the resultantmechanical strength of the fired or sintered LTCC body with flexuralstrength being the key strength parameter. Because of the strengthrequirement, one or more inorganic pigment may be used in a given LTCCslurry composition to provide a family of balanced properties but notlimited to optical (light reflectivity, predetermined color), mechanical(flexural strength), chemical (resistance to environmental corrosion),and thermal (ability to conduct heat) aspect. For example, a white colorLTCC chip carrier to provide a LED lighting module requires adequatestrength and white light reflectivity. Titanium dioxide, especially inthe tetragonal crystalline form of rutile, has a refractive index of 2.9and is among the top candidates to provide the required opticalperformance. However, titanium dioxide's flexural strength is about 140Mpa, about 50% of aluminum oxide, therefore, a volume % substitution ofaluminum oxide by titanium dioxide has to be done to maintain adequatestrength of the sintered body. A flexural strength of at least 150 Mpais preferred. Because the remnant glass phase and microstructure interms of crystalline phase, size, and grain boundary are all variantsaffecting the eventual strength of the sintered body, the LTCC slurrycomposition must be carefully adjusted to achieve the predeterminedobjective. Furthermore, a second inorganic white pigment, such aszirconium dioxide, can also be added to the slurry composition. Althoughthe refractive index of zirconium dioxide (2.16) is lower than titaniumdioxide (2.9 for rutile or 2.49 for anatase form), its potential toenhance mechanical strength provides a significant merit. For example,various types of modified zirconium dioxide or zirconium dioxide addedaluminum oxide exhibit superior flexural strength (quoted inparenthesis) as compared to a typical aluminum oxide (280 Mpa). Theseinclude and are not limited to yittria (Y2O3) doped tetragonal zirconiapolycrystals (y-TZP, 1,000 MPa), ceria (CeO2) doped tetragonal zirconiapolycrystals (c-TZP, 350 Mpa), zirconia toughened alumina (ZTA, 500Mpa), magnesia-partially stabilized zirconia (Mg-PSZ, 800 Mpa), amongothers.

Commonly available high temperature stable inorganic pigments includebut are not limited to Iron Oxide (red) such as Kroma Reds® fromElementis Pigments, Cobalt Chromite Green Spinel (green) such asShepherdcolor's Green 410, Cobalt Chromite Blue Green Spinel (green)such as Shepherdcolor's Green 201, Cobalt Titanate Green Spinel (green)such as Shepherdcolor's Green 10G663, Chromium Aluminate (green) such asFerro's CK14002, Chromium Cobalt Zinc (green) such as Ferro's CK14028,Cobalt Aluminate Blue Spinel (blue) such as Shepherdcolor's Blue 10K525,Cobalt Chromite Blue Green spinel (blue) such as Shepherdcolor's Blue10K579, Cobalt Aluminum Chromite (Blue) such as Ferro's CK15069, CobaltAluminum Zinc (blue) such as Ferro's CK15063, Cobalt Silicon (blue) suchas Ferro's CK220946, Chrome Antimony Titania Buff Rutile (yellow) suchas Shepherdcolor's Yellow 196, Nickel Antimony Titanium Yellow Rutile(yellow) such as Shepherdcolor's Yellow 10P110, . . . etc. Other optionsof pigments include but not limited to Mason Color's 6410 Canary(yellow), 6450 Praseodymium (yellow), 6204 Victoria Green (green), 6224Dark Green (green), 6263 Victoria (green), 6264 Victoria (green), 6306Vivid Blue (blue), 6350 Bright Blue (blue), 6360 Willow (blue), 6389Sapphire Blue (blue), 6003 Crimson (red), 6004 Crimson (red), 6090 Coral(red), and 6069 Dark Coral (red), . . . among others.

The advantages of using LTCC compositions include, but are not limitedto: (1) co-fireability at a range of temperature such as up to 850 to900° C. with high conductivity materials such as silver, copper, gold,and other alloys such as silver/platinum or silver/palladium; (2)formation of cavity structure to provide the platform for LED chipmounting and condensation of the emitted light, this include single chipor a multiplicity of chips of various display colors; (3) a closer TCEmatch of LTCC materials to the LED chips, (4) the choice of glass andrefractory inorganic oxide which provide mechanical strength suitablefor chip carrier application and next level module and packageintegration by soldering, wire bonding, and other electrical andmechanical attachment method; (5) suitable for multilayer circuit layoutto integrate with but not limit to at least one LED driver; (6) suitablefor providing electrical vias for circuit connection in an otherwiseinsulating dielectric materials; (7) suitable for providing thermalconduction vias which are co-fireable with the dielectric materialshaving superior thermal conductivity than a typical organic printedcircuit board substrate; and (8) suitable to be connected with at leastone heat sink by braze.

The glasses described herein are produced by conventional glass makingtechniques. The glasses were prepared in 500-1000 gram quantities.Typically, the ingredients are weighed then mixed in the desiredproportions and heated in a bottom-loading furnace to form a melt inplatinum alloy crucibles. Heating is conducted to a peak temperature(1300-1600° C.), depending on the glass composition and for a time suchthat the melt becomes entirely liquid and homogeneous. The glass meltswere quenched using a counter rotating stainless steel roller to form a10-20 mil thick platelet of glass. Alternatively, the glass melt can bequenched by direct draining into a water bath. For crystallizable glass,it is critical to assure a sufficiently high melt temperature to obtaina homogeneous melt and a sufficient cooling to prevent the formation ofpre-crystals. It may be necessary to apply water lancing to moreeffectively quench the glass melt. The resulting glass platelet was thenmilled to form a powder with its 50% volume distribution set between 1-5microns. The glass powders were then formulated with filler and organicmedium to cast tapes as detailed in the Examples section. The glasscompositions shown in Table 1 represent a broad variety of glasschemistry (high amounts of glass former to low amounts of glass former).The glass former oxides are typically small size ions with high chemicalcoordination numbers such as SiO₂, B₂O₃, and P₂O₅. The remaining oxidesrepresented in the table are considered glass modifiers andintermediates.

Two criteria used to identify the suitable candidate oxide(s) are highrefractive index and mechanical strength. A refractive index in therange of 1.5 to 3.5 is preferred. These include but not limit to thefollowing family of materials in a descending order of theircorresponding reflective index quoted in parenthesis: titanium oxide(2.64), zinc sulfite (2.37), calcium fluoantimonate (2.20), zirconiumoxide (2.16), lead arsenate (2.14), antimony trioxide (2.09), tin oxide(2.04), zirconium silicate (2.00), zinc spinel (1.90), and aluminumoxide (1.62). Among the above, Al₂O₃ is the preferred ceramic fillersince it reacts with the glass to form an Al-containing crystallinephase. Al₂O₃ is very effective in providing high mechanical strength andinertness against detrimental chemical reactions. For example, theflexural strength of Al₂O₃ or TiO₂ is, respectively, 345 or 140 MPa.Therefore, alumina is chosen as the preferred filler which can be usedas the sole refractory ceramic oxide or with at least one of the aboveoxides to provide color and/or light reflectivity while maintaining asuitable mechanic strength of the chip carrier package.

The above filler or mixtures thereof may be added to the castablecompositions used to form the tapes in an amount of 0-50 wt. % based onweight of the solids. Other materials, such as zirconium silicate andbarium titanate are also suitable ceramic filler candidates. Dependingon the type of filler, different crystalline phases are expected to formafter firing. The filler can control dielectric constant and loss overthe frequency range. For example, the addition of BaTiO₃ can increasethe dielectric constant significantly. A broad range of LTCCcompositions is applicable.

Another function of the ceramic filler is rheological control of theentire system during firing. The ceramic particles limit flow of theglass by acting as a physical barrier. They also inhibit sintering ofthe glass and thus facilitate better burnout of the organics. Otherfillers, α-quartz, CaZrO₃, mullite, cordierite, forsterite, zircon,zirconia, BaTiO₃, CaTiO₃, MgTiO₃, SiO₂, amorphous silica or mixturesthereof may be used to modify tape performance and characteristics. Itis preferred that the filler has at least a bimodal particle sizedistribution with D50 of the larger size filler in the range of 1.5 and3 microns and the D50 of the smaller size filler in the range of 0.3 and0.8 microns.

In the formulation of the tape compositions, the amount of glassrelative to the amount of ceramic material is important. A filler rangeof 30%-60% by weight is considered desirable in that the sufficientdensification is achieved. If the filler concentration exceeds 50% bywt., the fired structure may not be sufficiently densified and may betoo porous and mechanically weak. Within the desirable glass/fillerratio, it will be apparent that, during firing, the liquid glass phasewill become saturated with filler material.

For the purpose of obtaining higher densification of the compositionupon firing, it is important that the inorganic solids have smallparticle sizes. In particular, substantially all of the particles shouldnot exceed 15 μm and preferably not exceed 10 μm. Subject to thesemaximum size limitations, it is preferred that at least 50% of theparticles, both glass and ceramic filler, be greater than 1 μm and lessthan 6 μm.

The organic medium in which the glass and ceramic inorganic solids aredispersed is comprised of a polymeric binder which is dissolved in avolatile organic solvent and, optionally, other dissolved materials suchas plasticizers, release agents, dispersing agents, stripping agents,antifoaming agents, stabilizing agents and wetting agents.

To obtain better binding efficiency, it is preferred to use at least 5%wt. polymer binder for 90% wt. solids, which includes glass and ceramicfiller, based on total composition. However, it is more preferred to useno more than 30% wt. polymer binder and other low volatility modifierssuch as plasticizer and a minimum of 70% inorganic solids. Within theselimits, it is desirable to use the least possible amount of polymerbinder and other low volatility organic modifiers, in order to reducethe amount of organics which must be removed by pyrolysis, and to obtainbetter particle packing which facilitates full densification uponfiring.

Various polymeric materials have been employed as the binder for greentapes, e.g., poly(vinyl butyral), poly(vinyl acetate), poly(vinylalcohol), cellulosic polymers such as methyl cellulose, ethyl cellulose,hydroxyethyl cellulose, methylhydroxyethyl cellulose, atacticpolypropylene, polyethylene, silicon polymers such as poly(methylsiloxane), poly(methylphenyl siloxane), polystyrene, butadiene/styrenecopolymer, polystyrene, poly(vinyl pyrollidone), polyamides, highmolecular weight polyethers, copolymers of ethylene oxide and propyleneoxide, polyacrylamides, and various acrylic polymers such as sodiumpolyacrylate, poly(lower alkyl acrylates), poly(lower alkylmethacrylates) and various copolymers and multipolymers of lower alkylacrylates and methacrylates. Copolymers of ethyl methacrylate and methylacrylate and terpolymers of ethyl acrylate, methyl methacrylate andmethacrylic acid have been previously used as binders for slip castingmaterials.

U.S. Pat. No. 4,536,535 to Usala, issued Aug. 20, 1985, incorporatedherein by reference, has disclosed an organic binder which is a mixtureof compatible multipolymers of 0-100% wt. C₁₋₈ alkyl methacrylate,100-0% wt. C₁₋₈ alkyl acrylate and 0-5% wt. ethylenically unsaturatedcarboxylic acid of amine. Because the above polymers can be used inminimum quantity with a maximum quantity of dielectric solids, they arepreferably selected to produce the dielectric compositions of thisinvention.

Frequently, the polymeric binder will also contain a small amount,relative to the binder polymer, of a plasticizer that serves to lowerthe glass transition temperature (Tg) of the binder polymer. The choiceof plasticizers is determined by the polymer that needs to be modified.Among the plasticizers that have been used in various binder systems arediethyl phthalate, dibutyl phthalate, dioctyl phthalate, butyl benzylphthalate, alkyl phosphates, polyalkylene glycols, glycerol,poly(ethylene oxides), hydroxyethylated alkyl phenol,dialkyldithiophosphonate, polypropylene glycol dibenzoate andpoly(isobutylene). Of these, butyl benzyl phthalate is most frequentlyused in acrylic polymer systems because it can be used effectively inrelatively small concentrations. The plasticizer is used to prevent tapecracking and provide wider latitude of as-coated tape handling ability,such as blanking, printing, and lamination. A preferred plasticizer isBENZOFLEX® 400 manufactured by Rohm and Haas Co., which is apolypropylene glycol dibenzoate.

The solvent component of the casting solution is chosen so as to obtaincomplete dissolution of the polymer and sufficiently high volatility toenable the solvent to be evaporated from the dispersion by theapplication of relatively low levels of heat at atmospheric pressure. Inaddition, the solvent must boil well below the boiling point or thedecomposition temperature of any other additives contained in theorganic medium. Thus, solvents having atmospheric boiling points below150° C. are used most frequently. Such solvents include acetone, xylene,methanol, ethanol, isopropanol, methyl ethyl ketone, ethyl acetate,1,1,1-trichloroethane, tetrachloroethylene, amyl acetate, 2,2,4-triethylpentanediol-1,3-monoisobutyrate, toluene, methylene chloride andfluorocarbons. Individual solvents mentioned above may not completelydissolve the binder polymers. Yet, when blended with other solvent(s),they function satisfactorily. A particularly preferred solvent is ethylacetate since it avoids the use of environmentally hazardouschlorocarbons.

Application

A green tape for this invention is formed by casting a thin layer of aslurry dispersion of the glass, ceramic filler, polymeric binder andsolvent(s) as described above onto a flexible substrate, heating thecast layer to remove the volatile solvent. There is no limitation of thegreen tape thickness so long as adequate drying of either volatileorganic solvent(s) or water (in case of a water based organic bindersystem) can be achieved during the tape coating process. A preferablethickness range is between 5 and 30 mils, the lower limit is to providesufficient green strength for ease of handling and the upper limit is toprovide adequate drying of the solvent during tape casting. Furthermore,it is noted that the use of thicker tape minimizes the processing stepwhereas the use of thinner tape permits a higher degree of circuitintegration within the dimensional requirements of the chip carrier. Itis also noted that the solid content and viscosity of a slip are to beadjusted to coat LTCC tape of various “green” thickness, with extra careto be taken when the tape thickness exceeds 15 mils to assure properdrying of volatile solvent(s). The tape is then blanked into sheets orcollected in a roll form. The green tape is typically used as adielectric or insulating material for multilayer electronic circuits.

According to the defined configuration of the laminate, the selectedtapes are blanked with corner registration holes into sheets ofdimensions ranging from 3″×3″ to 6″×6″ or larger sizes. These green tapesheets are typically used as the dielectric or insulating material formultilayer electronic circuits. To connect various layers of themultilayer circuit, via holes are formed in the green tape. This istypically done by mechanical punching. However, a sharply focused lasercan also be used to volatilize the organic substance and form via holesin the green tape. Typical via hole sizes for electrical circuitconnection range from 0.004″ to 0.25″, and typical via hole sizes forheat dissipation range from 0.010″ to 0.050″ wherein circular via holesare normally applied. It is noted that this invention also extends tovia holes of other than circular shape according to the preferred designof the chip carrier structure and dimension. The interconnectionsbetween layers are formed by filling the via holes with a thick filmconductive composition. This composition is usually applied by screenprinting, stencil printing, or bladder filling. Each layer of circuitryis completed by screen printing conductor tracks. Also, when othercircuit function and integration is needed, resistor compositions orhigh dielectric constant compositions may be printed on selectedlayer(s) to form resistive or capacitive circuit elements. Furthermore,specially formulated high dielectric constant green tapes similar tothose used in the multilayer capacitor industry can be incorporated aspart of the multilayer circuitry. After each layer of the circuit iscompleted, the individual layers are collated and laminated. A confineduniaxial or isostatic pressing die is used to insure precise alignmentbetween layers. Firing is carried out in a standard thick film conveyorbelt furnace or in a box furnace with a programmed heating cycle. Thismethod will, also, allow top or bottom conductors to be co-fired as partof the sintered LTCC structure. The parts were then evaluated forstructural integrity and fired dimension against the specifications ofchip carriers.

As used herein, the term “firing” means heating the assemblage in anoxidizing atmosphere such as air to a temperature, and for a timesufficient to pyrolyze (burn-out) all of the organic material in thelayers of the assemblage to sinter any glass, metal or dielectricmaterial in the layers and thus densify the entire laminate. In thecases with copper based conductors, the furnace firing atmosphere is tobe optimized for adequate organic burnout and conductor and tapesintering. The former process needs oxidizing atmosphere such as air oroxygen doped nitrogen and the later process is normally done in nitrogenwith low oxygen content such as 100 ppm or below.

It will be recognized by those skilled in the art that in each of thelaminating steps the layers must be accurate in registration so that thevias are properly connected to the appropriate conductive path of theadjacent functional layer.

The term “functional layer” refers to the printed green tape, which hasconductive, resistive or capacitive functionality. Thus, as indicatedabove, a typical green tape layer may have printed thereon one or moreresistor circuits and/or capacitors as well as conductive circuits.

Thick Film Conductor Composition

A typical thick film composition for use in low temperature co-firedceramic circuits comprises, based on weight percent total thick filmcomposition: (a) 60-90 weight percent finely divided particles selectedfrom noble metals, alloys of noble metals and mixtures thereof; (b) oneor more inorganic binders selected from (1) 0.2-20 weight percent of oneor more refractory glass compositions, (2) 0.1-5 weight percent of anadditional inorganic binder selected from (i) metal oxides of Zn, Mg,Co, Al, Zr, Mn, Ni, Cu, Ta, W. La and other “glass network-modifying”refractory metal oxides, (ii) precursors of metal oxides; (iii)non-oxide borides; (iv)non-oxide suicides; and (v) mixtures thereof, and(3) mixtures thereof; dispersed in (c) 10-30 weight percent organicmedium.

A typical multilayer LTCC circuit substrate is fabricated by the use ofconductive elements comprising a nonconductive LTCC ceramic substratehaving a conductive pattern and connecting or non connecting via-fillconductive pattern affixed thereon formed by printing a pattern ofabove-described screen-printable and/or stencil-applicable paste andfiring the printed and/or laminated LTCCs to effect volatization of theorganic medium and liquid phase sintering of the inorganic materials andmetallization. Furthermore, the multilayer LTCC circuit substratefabrication is directed to a process for making conductors alone and/orin conjunction with via-fills comprising: (a) applying patterned thickfilm of the above-described screen-printable paste to a non conductiveceramic substrate, (b) drying the film at a temperature below 200° C.,more commonly at or below 150° C. and (c) firing the dried film toeffect liquid phase sintering of the inorganic materials andmetallization. For copper based conductor compositions, the co-firing ofmetallization with LTCC must be performed in an atmosphere such asnitrogen or other reducing atmosphere with or without oxygen dopingafter the completion of organic burnout which occurs normally at around450° C. or below. The components of a typical conductor composition arediscussed herein below. While specific examples of thick film conductorcompositions are identified here, it is understood by those skilled inthe art that a multitude of thick film conductors may be used in thepresent invention depending upon the application and desired properties.Several silver-based inner conductor compositions useful in the presentinvention include Product Numbers 6142d, 6145, 6148, 6154, 6742available from E. I. du Pont de Nemours and Company. Several useful viacompositions include Product Numbers 6141 and 6151 also available fromE. I. du Pont de Nemours and Company.

A. Conductive Material

The finely divided metals used in the invention can be of those selectedfrom noble metal, alloys of noble metals, and mixtures thereof, many ofwhich are commercially available. Furthermore, particle size andmorphology of the above-mentioned metal powders should be appropriate inscreen-printing and/or stencil-applying over non-fired ceramic tape ofthickness between 2 mils to 20 mils and preferably between 2 mils to 10mils and to the laminating conditions of the composite and to the firingconditions.

Thus the metal powders should be no bigger than 10 um and preferablyshould be below about 5 um. As a practical matter, the availableparticle size of the metals is from 0.1 to 10 um for silver or copper,depending on the specific application.

The metal powders can have either flake or non-flake morphology. Thenon-flake powders can be irregularly shaped or spherical. Such flakesilvers have an average surface area of approximately 1 m2/g and solidcontents of approximately 99-100% by weight. Non-flake silver powderstypically have an average surface area to weight ratio of 0.1-2.0 m2/gand solid contents of approximately 99-100% by weight.

In one embodiment of the present invention spherical metallic powdersare utilized. These spherical metallic powders, when packed have agreater particle-to-particle contact versus flake and other shapedpowders, which gives rise to a metal-to-metal contact and thus arelatively continuous flow of electrons for conduction when combinedwith the other components of the present invention. These closely packedmetal spherical particles allow for “tetrahedral” and/or “octrahedral”voids, wherein the specific inorganic binders of the present invention,such as metal oxides and/or glasses described below of relativelysmaller sizes, may settle and upon processing the inorganic binderssoften and hold the structure together in a uniform honeycomb-typestructure with superior metal-to-metal contact and more continuouselectron flow as compared to prior art compositions. In one embodiment,spherical metallic particles with an average particle size distributionin the range of 1 to 4 microns are preferred. In another embodiment, anaverage particle size of 2 to 3 microns is preferred. By using a blendof two metallic particles having distinctively different averagedparticle size, or likewise, a metallic particle with bimodal particlesize distribution, one can obtain a higher packing density leading toeffective sintering without significant volumetric shrinkage.Furthermore, a more smooth fired metallized surface can be attainedwhich provides a higher reflectivity of the LED display.

B. Inorganic Glass Binder

The inorganic binders of the present invention are one or more inorganicbinders selected from (1) 0.2-20 weight percent in the said pastecomposition of one or more refractory glass compositions with alogarithmic viscosity in the range of 6-7.6 at the firing temperature ofsaid circuit, (2) 0.1-5 weight percent of an additional inorganic binderselected from (i) metal oxides, (ii) precursors of metal oxides; (iii)non-oxide borides; (iv) non-oxide suicides; and (v) mixtures thereof,and (3) mixtures thereof.

The glass component of the conductor compositions of this invention isa, high-softening point, high viscosity glass at 0.2-20 weight percentlevel and, preferably, at 1-15 weight percent level.

As used herein, the term high-softening point glass is one having asoftening point 600-950° C., preferably, 750-870° C. as measured by theparallel plate viscosity measuring techniques (ASTM method).

Typical examples of glasses can be found from any of the compositionslisted in Table 1.

The glasses are prepared by conventional glass-making techniques, bymixing the desired components in the desired proportions and heating themixture to form a melt. As is well-known in the art, heating isconducted to a peak temperature and for a time such that the meltbecomes entirely liquid and homogenous. In the present work thecomponents are premixed in a polyethylene jar with plastic balls andmelted in a platinum crucible at 1200-1400° C. The melt is heated at thepeak temperature for 1-1.5 hours. The melt is then poured into coldwater. The maximum temperature of the water during quenching is kept aslow as possible by increasing the volume of water to melt ratio. Thecrude frit, after separation from water, is freed from residual water bydrying in air or displacement of water by rinsing with methanol, orother suitable method. The crude frit is then ball-milled for 6-7 hoursin a typical container with refractory lining using alumina grindingmedia in water or a typical organic solvent such as isopropanol. Afterdischarging the milled slurry from the mill, the excess water or solventis removed by decantation and the frit powder is hot air-dried. Thedried powder is then screened through a 325 mesh screen to remove anylarge particles.

The two major properties of the frits are: it aids the sintering of theconductive metal particulate matters and minimizes the intermixing ofconductor materials with remnant glasses present in the LTCC ceramics.

C. Metal Oxide/Non-oxide Binder

The metal oxides and non-oxides, such as borides and silicides, whichare suitable for the practice of the invention are those which arecapable of reacting with remnant glasses of the tape and increasing theviscosity of the remnant glasses when the composition of the inventionis cofired with the tape, either on the surface or buried. Additionallythe binders useful in the present invention should act as “sinteringinhibitors” for the metal powders during firing of the system.

Suitable inorganic oxides are those based on Zn2+, Mg2+, Co2+, Al3+Zr4+,Mn2+, Ni2+, Cu2+, Ta3+, W4+, La3+and other “glass network modifying”refractory oxides and complex oxides such as copper bismuth ruthenate,and organometallic compounds such as organotitanate disclosed in U.K.Pat. No. 772,675 and U.S. Pat. No. 4,381,945, incorporated herein, thatwill decompose into finely divided powders of metal oxides during thefiring of the system.

The particle size of the metal oxides or precursors should beappropriate to be used in the said paste composition for screen and/orstencil printing, thus the particle size should be no larger than 15 umand preferably should be below 5 um.

D. Organic Medium

The inorganic components including metal powders, glass binder, andmetal oxide or non-oxide binder are typically dispersed into an organicmedium by mechanical mixing to form viscous compositions called “pastes”having suitable consistency and rheology for printing. A wide variety ofinert liquids can be used as organic medium. The rheological propertiesof the medium must be such that they lend good application properties tothe composition, including: stable dispersion of solids, appropriateviscosity and thixotropy for screen printing, acceptable unfired “green”strength, appropriate wettability of the substrate and the paste solids,a good drying rate, and good firing and burn out properties. The organicmedium is typically a solution of polymer(s) in solvent(s).Additionally, a small amount of additives, such as surfactants, may be apart of the organic medium. The most frequently used polymer for thispurpose is ethyl cellulose. Other examples of polymers includeethylhydroxyethyl cellulose, wood rosin, mixtures of ethyl cellulose andphenolic resins, polymethacrylates of lower alcohols, and monobutylether of ethylene glycol monoacetate can also be used. The most widelyused solvents found in thick film compositions are ester alcohols andterpenes such as alpha- or beta-terpineol or mixtures thereof with othersolvents such as kerosene, dibutylphthalate, butyl carbitol, butylcarbitol acetate, hexylene glycol and high boiling alcohols and alcoholesters. In addition, volatile liquids for promoting rapid hardeningafter application on the substrate can be included in the vehicle.Various combinations of these and other solvents are formulated toobtain the viscosity and volatility requirements desired.

The inorganic particles are mixed with an inert liquid medium (vehicleor medium) typically by mechanical mixing (e.g. on a roll mill) to forma paste-like composition having suitable consistency and rheology forscreen printing and/or stencil applying. The latter is printed as a“thick film” on LTCC green tapes in the conventional manner. Any inertliquid may be used as the vehicle. Various organic liquids, with orwithout the thickening and/or stabilizing agents and/or other commonadditives may be used as the vehicle. The only specific criteria of thevehicle is that it must be chemically compatible to the organics presentin the LTCC green tapes. Exemplary of organic liquids which can be usedare the aliphatic alcohols, esters of such alcohols, for example,acetates and propionates, terpenes such as pine oil, terpineol and thelike, texanol and the like, solutions of resins such as ethyl cellulosein solvents as pine oil, and the monobutyl ether of ethylene glycolmonoacetate.

The vehicle may contain volatile liquids to promote fast setting afterapplication to the tape.

The ratio of vehicle to solids in the dispersions can vary considerablyand depends upon the manner in which the dispersion is to be applied andthe kind of vehicle used and furthermore the use of the conductors arefor the conductor lines and/or via-fill conductor connections. Normallyto achieve good coverage the dispersions will comprise 60-98% solids and40-2% organic medium (vehicle). The compositions of the presentinvention may, of course, be modified by the addition of othermaterials, which do not affect its beneficial characteristics. Suchformulations are well within the skill of the art.

The conductor composition(s) of the present invention is used with thesaid LTCC glass-ceramic dielectric via the method described herein.

Formulation of Thick Film Compositions (Pastes)

The thick film compositions of the present invention were preparedaccording to the following general methodology. The inorganic solids aremixed with the organic medium and dispersed with suitable equipment,such as a three-roll mill, to form a suspension, resulting in acomposition for which the viscosity will be in the range of 100-200Pascal-seconds at a shear rate of 4 sec-1 for the line conductorcompositions and the corresponding value for via-fill conductors is1000-5000 Pascal-seconds.

In the examples, which follow, the formulation was carried out in thefollowing manner: The ingredients of the paste, minus about 2-5% of theorganic components, were weighed together in a container. The componentswere then vigorously mixed to form a uniform blend; then the blend waspassed through dispersing equipment, such as a three roll mill, toachieve a good dispersion of particles. A Hegman gauge was used todetermine the state of dispersion of the particles in the paste. Thisinstrument consists of a channel in a block of steel that is 25 um deep(1 mil) on one end and rams up to 0″ (i.e., 0-25 um range) depth at theother end. A blade was used to draw down paste along the length of thechannel. Scratches appeared in the channel where agglomerates' diameterwas greater than the channel depth. A satisfactory dispersion gave afourth scratch point of 10-18 um, typically. Fourth scratch measurementsof >20 um and half channel measurements of >10 um indicated a poorlydispersed suspension/paste.

Next, the remaining 2-5% of the organic components of the paste wasadded, and the resin content was adjusted to bring the viscosity of thecomposition to the desired value.

The composition was then applied to a substrate, in this particularcase, to the “green tape”. The “green tape” was formed by casting a 1-20mil, preferably 2-10 mil, thin layer of a slurry dispersion of the glassand ceramic filler fine particulates, polymeric binder(s) and solvent(s)as described in the art of “tape casting” into a flexible substrate, andheating the cast layer to remove the volatile solvent. The tape isblanked into sheets or provided in roll form. This green tape is used asan insulating substrate for multilayer electronic circuits/devices, inplace of conventional substrates, such as alumina and other refractoryceramic substrates. The green tape sheet is blanked with registrationholes at the four corners, and via holes to connect the different layersof conductors using mechanical punching. The size of via holes variesdepending on circuit design and property requirements. Theinterconnections of circuit between conductor track layers of the tapeare typically applied by screen printing the conductive inks in the viaholes.

The conductive line compositions of the present invention were appliedto a sheet of green tape, by the process of screen printing, to a wetthickness of about 10-30 um and the via holes were filled withrespective conductive via compositions.

After each layer of tape is printed with conductor lines and via holesas appropriate to the circuit design, the individual layers arecollated, laminated and pressed using uniaxial or isostatic pressing dieand techniques as described elsewhere in the art of tapepressing/lamination techniques. It will be recognized by those skilledin the art that in each of the laminating steps the printed tape layersmust be accurate in registration so that the vias are properly connectedto the appropriate conductive lines of the adjacent functional layer,and in the case of thermal vias, each via will be connectedappropriately to the next one.

Firing to effect sintering of the green tape compositions and of theinorganic binder as well as the finely divided particles of metal, ispreferably done in a well ventilated belt conveyor furnace or programmedbox furnace with a temperature profile that will allow de-polymerizationof polymers; and/or burnout of the organic matter at about 300-600° C. aperiod of maximum temperature of about 800-950° C. lasting about 5-20minutes, followed by a controlled cool down cycle to preventover-sintering and crystal growth, unwanted chemical reactions atintermediate temperatures, or substrate/fired ceramic tape fracture fromtoo rapid cool down. The overall firing procedure will preferably extendover a period of between 3.5 to 5 hours, and in certain cases it couldtake up to 24 hours or more depending on the number of layers of greentapes laminated together and/or the thickness of the green tape layers.

The fired thickness of the conductor can range from about 5 to about 15um, depending on the percent of solids, the type of screen thecomposition is printed with, the printer set up, and degree of sinteringof the inorganic solids. The thickness of via conductors vary dependingon the thickness of the green tape used and degree of sintering of thevia composition. In order to avoid two major defects, dimpling andposting of the vias, the selection of viscosity and solid content of thecomposition is important. In general, increased solid content couldresult in posting and lower solid content will result in dimpling.

The conductor compositions of this invention can be printed onto thegreen tapes, or onto other thick films either by using an automatedprinter or a hand printer in the conventional manner. Preferably,automation screen printing techniques are employed, using 200 to 325mesh screen with typically 0.5 mil emulsion thickness. Conventionalstencil printing techniques are also can be used, particularly forfilling the smaller vias of size 4-8 mils.

Specific Consideration on Conductor Compositions for Light Reflection

It is commonly known that a frit-containing surface conductor provides arelatively higher electrical resistivity and a darker appearance.Therefore, for the purpose to provide light reflection, it is necessaryto use a glass-free Ag, Au, Cu, or alloyed Ag/Pt or Ag/Pd conductor,with or without oxide binder in order to provide reflection. The choiceof conductive powders such as Ag, Au, Cu, Pt, or Pd particle sizedistribution, packing density optimization are all important factorswhich contribute to the light reflectivity. Packing density optimizationcan be achieved by selecting conductor particles of at least one andpreferably more than one averaged particle size.

More specifically, a co-fireable silver based thick film conductorcomposition is deposited onto the surface surrounding the LED chip orchips located at the build-in cavity, such as a silver composition hasthe following characteristics including but not limited to

a) the averaged particle size of silver between 1 and 20 microns andpreferably between 1 and 5 microns,

b) the silver particles are with or without surface attached agentsincluding but not limited to phosphate ester, fatty acid, and the like.

c) at least one type of silver particles is used in the composition, inthe case of two or more silver particles, the choice of candidate silverparticles is dependent on their respective particle size distributionfor the purpose of minimizing the sintering stress versus the sinteringof LTCC dielectric materials;

d) at least one type of silver particles is used in the composition, inthe case of two or more silver particles, the choice of candidate silverparticles is dependent on their respective particle size distributionfor the purpose of minimizing the surface roughness to enhance the lightreflectivity of but not limited to a LED backlight module.

If needed, the conductor pads can be further plated to enhance the lightreflectivity.

Specific Consideration on Conductors for Thermal Vias

Thermal vias are used to dissipate the heat resulted from a functionalLED chip carrier package and this invention is to provide at least toone and preferably a multiplicity of thermal vias to minimize thejunction temperature to prolong the life of the HB LED packagefunctions. It is further noted that the thermal vias are normallyconnected to heat spreader pad which can take the shape and form of amesh pattern, a solid pattern, or any other suitable geometry.

Increased operational life in multilayered circuit substrates such asthe chip carriers of this invention generally can be achieved through ajudicious selection of materials and careful thermal-mechanicalmanagement and design. Typically, the efforts involve controlling thethermal profile in a populated LTCC (or other materials to producemultilayer circuit substrates) module by the choices of substrate, heatsink, and placement of the heat sink. Substantial reduction in junctiontemperatures can then be obtained, and the apparent increase inreliability generally suffices for the most if not all electronicapplications.

However, in high-speed multichip module design, other complicationsarise, such as the mixing of chips which may have different thermaldissipation characteristics. In this invention, the use of at leastthree LED chips, namely G, R, and B, present exactly the aforementionedchallenges. A possibly large disparity in junction temperatures altersthe switching thresholds of the chips, generates clock skew, anddegrades system performance. For cost reasons, higher thermalconductivity materials such as beryllia or aluminum nitride are notviable options to replace alumina. Furthermore, such an option does notcompletely solve the temperature equalization between chips of mixedtechnologies. The thermal conduction paths from chip to ambient arestill equivalent, and the dissipated power levels are still different.Current practice calls for introducing thermal vias in LTCC to lowerthermal impedance. It is to be noted, however, that the junctiontemperature disparity will still be observed if equal thermal viadensities are used. By adjusting the density of thermal vias, variablecooling can be designed within a large range of thermal impedance.Junction temperatures in chips with large power density can thus bebalanced. This method makes the best use of the lower thermalconductance of the LTCC dielectric materials and the high thermalconductance of the via fill conductor pastes to produce a wide range ofcomposite thermal impedance. This concept can be extended further to theselective cooling of different regions of a chip. Factors such as theuse of heat spreader (i.e. a metallized conductor plane be a solid orgridded geometry) and the ratio of chip bonding area to the availablecavity space both affect the thermal conduction performance. It is notedthat the maximum chip bonding area equal to the available cavity areaprovides the best thermal management. However, due to the actualfunctional consideration, the substrate and cavity dimension aretailored to each chip array and sufficient space is needed to form agood die attached fillet for adequate bonding. In the case of flip chipbonding or BGA attachment, minimum space between the chip and cavity canbe adopted so long as adequate electrical insulation between the anodeand cathode(s) is achieved. This differs from the use of wire bondingfor chip connection which needs more space in between. The effect ofintroducing thermal spreader will be described further in the followingteaching.

LTCC has inherently higher thermal conductivity than organic materialsand the thermal conductivity can be improved with the addition ofthermal vias and metallized conductor planes. There are two aspects, thethru-plane and the in-plane thermal conductivity to be addressed herein.Testing has shown an improvement in thru-plane conductivity to be 2times of more than that of the dielectric material conductivity andimprovement in in-plane thermal conductivity by 2 to 3 times through theuse of thermal vias and metallized planes. While solid metallizationplanes can be used in LTCC, gridded or meshed planes improveprocessability and they are as thermally effective as solid planes. Itis understood that the highest thru-plane thermal conductivity isobtained in the samples with the greatest possible number of thermalvias. The addition of any solid or gridded conductor planes does notsignificantly improve the thermal conductivity of a typically lower viadensity design, such as 12 mil vias on 50, 100, and 150 mil centers.However, the above conductor planes significantly improve the thermalconductivity of a typically higher via density design, such as 8 milvias on 20, 40, and 60 mil centers.

In a configuration without thermal vias the solid or gridded conductorplanes offer no improvement in thru-plane thermal conductivity. Theaddition of one internal gridded conductor plane improved the in-planethermal conductivity by about 10 to 20%. Furthermore, gridded planesconnecting thru thermal vias improve the in-plane thermal conductivityby about twice that of the configurations without conductor planes.

Brazing Materials and Process

Thick film brazing materials are suitable for large volume manufacturingand the attachment of heat sink to a pre-fired LTCC chip carrier. It isnoted that the temperature hierarchy of the HB LED package modulerequires (1) the co-firing of tape, conductor, electrical via, andthermal via which takes place at highest temperature such as 850 to 900°C., (2) brazing of chip carrier to a heat sink which takes placenormally at a medium temperature range between 350° C. and 850° C.,depending on the choice of braze materials, (3) chip bonding by flipchip or soldering, (4) gold wire bonding if necessary, and (5) applyingplastic encapsulant such as epoxy or other thermal plastic organicmaterials.

A brazing process normally is consisted of (1) brazing metallization,(2) brazing alloy/filler metal, (3) preparing the surface of joiningcomponent—a heat sink in this invention, (4) fixturing, (5) firing infurnace with suitable profile and atmosphere control. Proper thick filmbrazing compositions normally is consisted of a thick film adhesionlayer and a thick film barrier layer. For example, the DuPont thick filmbrazing materials include Au-based 5062 (adhesion layer), 5063 (barrierlayer), and Ag/Pt-based 5081 (adhesion layer) and 5082 (barrier layer).The above thick film compositions provide an interface between LTCC withthermal vias and a heat sink. Depending on the TCE, thermalconductivity, and cost, a variety of heat sink materials are availablefor the applications of this invention. These include but are notlimited to plated alloys of Cu—W, Cu—Mo, Cu—Mo—Cu, and Al—SiC; BeO andAlN are also good candidate materials for heat sink applications. Theheat sink may also be Al. Other examples include but are not limited toa metal core printed wiring (MCPWB).

EXAMPLES

Tape compositions used in the examples were prepared by ball milling thefine inorganic powders and binders in a volatile solvent or mixturesthereof. To optimize the lamination, the ability to pattern circuits,the tape burnout properties and the fired microstructure development,the following volume % formulation of slip was found to provideadvantages. The formulation of typical slip compositions is also shownin weight percentage, as a practical reference. The inorganic phase isassumed to have a specific density of 4.5 g/cc for glass and 4.0 g/ccfor alumina and the organic vehicle is assumed to have a specificdensity of 1.1 g/cc. The weight % composition changes accordingly whenusing glass and refractory oxides for light reflection enhancement otherthan alumina as the specific density maybe different than those assumedin this example. The table 1 lists a variety of lead-containing andlead-free glass compositions suitable for the applications in thisinvention.

TABLE 1 A List of glass compositions (in wt. %) Glass # (density) SiO₂Al₂O₃ PbO ZrO₂ B₂O₃ CaO BaO MgO Na₂O Li₂O P₂O₅ TiO₂ K₂O Cs₂O Nd₂O₃ SrO 1 (4.72) 6.08 23.12 4.50 34.25 32.05  2 (3.06) 13.77 4.70 26.10 14.0535.09 1.95 4.34  3 (2.66) 55.00 14.00 9.00 17.50 4.50  4 (4.54) 11.9121.24 0.97 4.16 26.95 4.59 30.16  5 (2.80) 56.50 9.10 17.20 4.50 8.000.60 2.40 1.70  6 (4.45) 11.84 21.12 1.31 4.14 25.44 6.16 29.99  7(2.52) 52.00 14.00 8.50 17.50 4.75 2.00 0.25 1.00  8 (4.58) 6.27 22.790.93 4.64 33.76 31.60  9 (4.56) 9.55 21.73 0.92 4.23 32.20 1.24 30.13 10(4.55) 10.19 21.19 0.97 4.15 28.83 4.58 30.08 11 (3.01) 12.83 4.65 21.7213.09 34.09 1.96 11.65 12 (3.01) 13.80 4.99 25.86 13.45 33.60 2.09 4.351.87 13 (2.61) 52.00 14.00 9.00 17.50 5.00 1.75 0.25 0.50 14 (2.53) 53.513.00 8.50 17.00 1.00 2.25 0.25 1.50 3.00 15 (3.02) 13.77 4.70 22.6014.05 35.09 1.95 7.84 16 (2.57) 54.00 12.86 8.41 16.82 0.99 2.23 0.251.48 2.96 17 (2.55) 54.50 12.72 8.32 16.63 0.98 2.20 0.24 1.47 2.94

Typical Primary and Internal Constraining Tape Compositions:

Volume % Weight % Inorganic phase 41.9 73.8 Organic phase 58.1 26.2The above volume and weight % slip composition may vary dependent on thedesirable quantity of the organic solvent and/or solvent blend to obtainan effective slip milling and coating performance. More specifically,the composition for the slip must include sufficient solvent to lowerthe viscosity to less than 10,000 centipoise; typical viscosity rangesare 1,000 to 8,000 centipoise, depending on the target as-coated tapethickness. An example of a slip composition is provided in Table 2.Depending on the chosen slip viscosity, higher viscosity slip prolongsthe dispersion stability for a longer period of time (normally severalweeks). A stable dispersion of tape constituents is usually preserved inthe as-coated tape.

TABLE 2 Tape Slip Compositions: Component Weight % Acrylate andmethacrylate polymers 4.6 Phthalate type plasticizers 1.1 Ethylacetate/isopropyl alcohol mixed solvent 20.4 Glass powder 50.7 Aluminapowder 23.2

The glasses used in the Examples were melted in PVRh crucibles at1450-1600° C. for about 1 hour in an electrically heated furnace.Glasses were quenched by metal roller as a preliminary step and thensubjected to particle size reduction by milling. The glass particleswere adjusted to a 5-7 micron mean size by milling prior to formulationas a slip. Since additional milling was utilized in the fabrication ofslip, the final mean size is normally in the range of 1-3 microns. It isnoted that the glass particles may also be pre-milled to a final size of1-3 microns prior to its use as an ingredient in the slip composition.

The percentage reflectance measurements were made using a Varian Cary5000 uv/vis/nir spectrophotometer with a DRA-2500 diffuse reflectanceaccessory. The DRA-2500 uses a 150mm integrating sphere coated withSpectralon®. A 100 percent baseline is then collected using Spectralon®reference. The reference is then replaced by the sample and thereflectance spectrum is collected. For the samples included in thefollowing example section, a wavelength range of 800 to 250 was used.Both diffuse and specular components were included in the measurement.

Example 1

A four layer LTCC laminate was prepared using the following materials:

Tape 1, as described above in Table 2 and with the inorganic powdercontaining 64 volume percent of a glass with the composition in weightpercent of glass #5 in Table 1 and 36 volume percent Al₂O₃. It is notedthat the glass #5 contains 17.20 weight % lead oxide. By weight % of thetotal inorganic composition, glass #5 or alumina is respectively,55.44%, or 44.56%. It is further noted that inorganic pigments providingwhite color can also be used to substitute a portion of the alumina, asdescribed in Tape 2 to enhance the light reflectivity of the upperportion of the resultant LTCC chip carrier. The green thickness was 10mils or 254 rriicrometers.

After lamination the parts were placed on setters and fired in aconveyer furnace with an air atmosphere where the temperature wasincreased from room temperature to 850° C. and held for 18 minutes andthen allowed to cool back to room temperature the whole process takingapproximately 3 hours and 30 minutes. The fired part was fully densifiedand free from camber.

Example 2

A four layer LTCC laminate was prepared using the following materials:

Tape 2, as described above in Table 2 and with the inorganic powdercontaining 64 volume percent of a glass with the composition in weightpercent of glass #5 and 36 volume percent of Al₂O₃ and TiO₂ at a ratioof 10 to 1. By weight % of the total inorganic composition, glass #5,alumina, or titania, is respectively, 55.44%, 40.10%, or 4.46%. Thegreen thickness was 10 mils or 254 micrometers.

After lamination the parts were placed on setters and fired in aconveyer furnace with an air atmosphere where the temperature wasincreased from room temperature to 850° C. and held for 18 minutes andthen allowed to cool back to room temperature the whole process takingapproximately 3 hours and 30 minutes. The fired part was fully densifiedand free from camber.

Example 3

A four layer LTCC laminate was prepared using the following materials:

Tape 3, as described above in Table 2 and with the inorganic powdercontaining 68.7 volume percent of a glass with the composition in weightpercent of glass #17 and 31.3 volume percent of Al₂O₃, glass #17, Theweight % composition of frit or alumina is respectively, 58.51%, or41.49%. The green thickness was 10 mils or 254 micrometers.

After lamination the parts were placed on setters and fired in aconveyer furnace with an air atmosphere where the temperature wasincreased from room temperature to 850° C. and held for 18 minutes andthen allowed to cool back to room temperature the whole process takingapproximately 3 hours and 30 minutes. The fired part was fully densifiedand free from camber.

The % light reflection the above blank LTCC substrate at red (650 nm),green (510 nm), or blue (475 nm) light wavelength is, respectively,82.1%, 81.1 % or 80.9% when measuring the top surface of the fired partwith respect to how the substrate was placed on the setter for thefurnace firing.

Example 4

A four layer LTCC laminate was prepared using the following materials:

Tape 4, as described above in Table 2 and with the inorganic powdercontaining 68.7 volume percent of a glass with the composition in weightpercent of glass #17 and 31.3 volume percent of Al₂O₃ and TiO₂ at aratio of 98 to 2. The weight % composition of frit, alumina, or TiO₂ isrespectively, 58.51%, 40.63%, or 0.86%. The green thickness was 10 milsor 254 micrometers.

After lamination the parts were placed on setters and fired in aconveyer furnace with an air atmosphere where the temperature wasincreased from room temperature to 850° C. and held for 18 minutes andthen allowed to cool back to room temperature the whole process takingapproximately 3 hours and 30 minutes. The fired part was fully densifiedand free from camber.

The % light reflection the above blank LTCC substrate at red (650 nm),green (510 nm), or blue (475 nm) light wavelength is, respectively,82.8%, 82.7% or 81.9% when measuring the top surface of the fired partand 82.8%, 82.5%, or 81.6% when measuring the bottom surface of thefired part with respect to how the substrate is placed on the setter forthe furnace firing.

Example 5

A four layer LTCC laminate was prepared using the following materials:

Tape 5, as described above in Table 2 and with the inorganic powdercontaining 68.7 volume percent of a glass with the composition in weightpercent of glass #17 and 31.3 volume percent of Al₂O₃ and TiO₂ at aratio of 90 to 10. The weight % composition of frit, alumina, or TiO₂ isrespectively, 58.51%, 37.17%, or 4.32%. The green thickness was 10 milsor 254 micrometers.

After lamination the parts were placed on setters and fired in aconveyer furnace with an air atmosphere where the temperature wasincreased from room temperature to 850° C. and held for 18 minutes andthen allowed to cool back to room temperature the whole process takingapproximately 3 hours and 30 minutes. The fired part was fully densifiedand free from camber.

The % light reflection the above blank LTCC substrate at red (650 nm),green (510 nm), or blue (475 nm) light wavelength is, respectively,92.5%, 89.6% or 86.7% when measuring the top surface of the fired partand 92.3%, 88.8%, or 84.9% when measuring the bottom surface of thefired part with respect to how the substrate is placed on the setter forthe furnace firing.

Example 6

A four layer LTCC laminate was prepared using the following materials:

Tape 6, as described above in Table 2 and with the inorganic powdercontaining 64 volume percent of a glass with the composition in weightpercent of glass #17 and 36 volume percent of Al₂O₃ and TiO₂ at a ratioof 5 to 1. By weight % of the total inorganic composition, glass #17,alumina, or titania, is respectively, 53.12%, 39.06%, or 7.82%. Thegreen thickness was 10 mils or 254 micrometers.

After lamination the parts were placed on setters and fired in aconveyer furnace with an air atmosphere where the temperature wasincreased from room temperature to 850° C. and held for 18 minutes andthen allowed to cool back to room temperature the whole process takingapproximately 3 hours and 30 minutes. The fired part was fully densifiedand free from camber.

Example 7

A four layer LTCC laminate was prepared using two layers of Tape 1 andtwo layers of Tape 2 wherein the green thickness of both tapes was 10mils or 254 micrometers. Tape 2, as described above in Example 2 isconsisted of TiO₂ which provides light reflection enhancement and wasplaced as the top two layers of the LTCC laminate.

After lamination the parts were placed on setters and fired in aconveyer furnace with an air atmosphere where the temperature wasincreased from room temperature to 850° C. and held for 18 minutes andthen allowed to cool back to room temperature the whole process takingapproximately 3 hours and 30 minutes. The fired part was fully densifiedand free from camber.

Example 8-14

In the Examples 8-14 that follow, the glass compositions detailed inTable 1 were used. Glasses 2, 5, and 6 represent glasses that are usefulin the present invention. It is noted that both lead-containing andlead-free glasses are applicable to be the inorganic binder in thepreferred conductor paste compositions.

Conductor compositions: Examples 8-14 represent examples of the presentinvention. All formulations are given in weight percent of the totalthick film composition. Non-flake silver powders represented below havean average surface area to weight ratio of 0.1-2.0 m2/g. Palladium metalpowders represented below have an average surface area to weight ratioof 2.0-15.0 m2/g. Platinum metal powders represented below have anaverage surface area to weight ratio of approximately 10 m2/g to 30m2/g. The average particle size distribution of the gold metal powdersis in the range of 1-4 microns.

Example 8

Silver Ground Plane & Inner Conductor Silver powder 80.6 Frit #2 1.2Organo metallics 1.0Ethyl cellulose/texanol-based medium represents the balance

-   Silver powder SA 0.1-1.5 m2/gm

Example 9

Silver Palladium Solderable Top Conductor Silver powder 53.5 Palladiumpowder 13.6 Copper bismuth ruthenate 5.1 Copper oxide 0.5Ethylcellulose/terpineol-based medium represents the balance

-   Flake Silver SA ˜0.60-0.90 m2/gm; Tap density 4.0-6.0 g/ml

Example 10

Silver via fill Conductor Silver Powder 90.9 Frit #2 1.2Ethyl cellulose/texanol-based medium represents the balance

-   Silver powder SA 0.1-1.5m2/gm

Example 11

Wire-Bondable/Inner/Ground plane Gold Conductor Gold powder 80.7 Frit #50.8Ethyl cellulose/terpineol-based medium represents the balance

-   Gold powder particle size distribution (PSD) d50˜2-3 um

Example 12

Palladium-Silver Transition via Fill Conductor for mixed metal systemSilver Powder 86.5 Palladium powder 3.0 Frit # 5 0.8Ethyl cellulose/texanol-based medium represents the balance

-   Palladium powder surface area to weight ratio (SA) ˜1.1-1.7 m2/gm-   Silver powder SA ˜0.1-1.5 m2/gm

Example 13

Silver-Platinum Platable Conductor Silver Powder 82.2 Platinum 2.0 Frit#17 0.8Ethyl cellulose/texanol-based medium represents the balance

-   Palladium powder SA ˜1.1-1.7 m2/gm-   Platinum Powder SA ˜0.7-1.2 m2/gm

Example 14

Wire-bondable Top Conductor For “Mixed metal system” Gold powder 78.0Frit #17 0.7Ethyl cellulose/terpineol-based medium represents the balance

-   Gold powder PSD ˜d50 4-5 um

Example 15

Silver-Paladium Solderable Conductor Silver Powder 51.0 Paladium 13.0Ethyl cellulose/texanol-based medium represents the balance

-   Silver powder has irregular shape with a D50 particle size of 2.5 μm-   The % light reflection the above metallization after co-firing with    LTCC chip carrier at red (650 nm), green (510 nm), or blue (475 nm)    light wavelength is, respectively, 49.4%, 42.2% or 40.7%.

Example 16

Silver Conductor Silver Powder 57.8 Cuprous oxide 1.0 Frit #17 5.4Ethyl cellulose/texanol-based medium represents the balance

-   Silver powder has irregular shape with a D50 particle size of 2.5 μm-   The % light reflection the above metallization after co-firing with    LTCC chip carrier at red (650 nm), green (510 nm), or blue (475 nm)    light wavelength is, respectively, 67.4%, 65.7% or 64.6%.

Example 17

Silver Via Fill Conductor Silver Powder 87.6Ethyl cellulose/texanol-based medium represents the balance

-   Silver powder has spherical shape with a D50 particle size of 2.5 μm-   The % light reflection the above metallization after co-firing with    LTCC chip carrier at red (650 nm), green (510 nm), or blue (475 nm)    light wavelength is, respectively, 94.4%, 88.9% or 85.3%.

Example 18

Silver Inner Signal Conductor Silver Powder 65.0 Frit #5 3.0Ethyl cellulose/texanol-based medium represents the balance

-   Silver powder has irregular shape with a D50 particle size of 2.5 μm-   The % light reflection the above metallization after co-firing with    LTCC chip carrier at red (650 nm), green (510 nm), or blue (475 nm)    light wavelength is, respectively, 94.2%, 92.0% or 91.3%.

Example 19

Silver Inner Signal Conductor Silver Powder type A 26.1 Silver Powdertype B 55.6 Frit #5 1.2Ethyl cellulose/texanol-based medium represents the balance

-   30 Each of silver powders type A or B both has irregular shape with    a D50 particle size of 2.5 μm or 8.2 μm, respectively-   The % light reflection the above metallization after co-firing with    LTCC chip carrier at red (650 nm), green (510 nm), or blue (475 nm)    light wavelength is, respectively, 95.4%, 91.9% or 91.2%.

Example 20

Silver Inner Signal Conductor Silver Powder 77.0Ethyl cellulose/texanol-based medium represents the balance

-   Silver powder has flake shape with a D50 particle size of 2.4 μm-   The % light reflection the above metallization after co-firing with    LTCC chip carrier at red (650 nm), green (510 nm), or blue (475 nm)    light wavelength is, respectively, 97.9%, 96.4% or 95.4%.

Example 21

Silver Inner Signal Conductor Silver Powder 77.0 Frit #17 0.5Ethyl cellulose/texanol-based medium represents the balance

-   Silver powder has flake shape with a D50 particle size of 2.4 μm-   The % light reflection the above metallization after co-firing with    LTCC chip carrier at red (650 nm), green (510 rim), or blue (475 nm)    light wavelength is, respectively, 95.4%, 92.5% or 91.2% when silver    was fired upward, and 95.0%, 91.8%, or 90.3% when silver was fired    downward (i.e. facing the setter).

Example 22

Silver Inner Signal Conductor (DuPont 6742) Silver Powder 77.0Ethyl cellulose/texanol-based medium represents the balance

-   Silver powder has irregular shape with a D50 particle size of 8.2 μm-   The % light reflection the above metallization after co-firing with    LTCC chip carrier at red (650 nm), green (510 nm), or blue (475 nm)    light wavelength is, respectively, 98.0%, 96.3% or 95.5%.

Example 23

Silver Inner Signal Conductor Silver Powder 77.0 Frit #17 0.5Ethyl cellulose/texanol-based medium represents the balance

-   Silver powder has irregular shape with a D50 particle size of 8.2 μm-   The % light reflection the above metallization after co-firing with    LTCC chip carrier at red (650 nm), green (510 nm), or blue (475 nm)    light wavelength is, respectively, 95.3%, 92.2% or 91.0% when silver    was fired upward, and 94.0%, 90.4%, or 88.9% when silver was fired    downward (i.e. facing the setter).

Example 24

Silver Inner Signal Conductor Silver Powder 77.0Ethyl cellulose/texanol-based medium represents the balance

-   Silver powder has flake shape with a D50 particle size of 3.7 μm-   The % light reflection the above metallization after co-firing with    LTCC chip carrier at red (650 nm), green (510 nm), or blue (475 nm)    light wavelength is, respectively, 98.2%, 96.6% or 95.5%.

Example 25

Silver Inner Signal Conductor Silver Powder 77.0 Frit #17 0.5Ethyl cellulose/texanol-based medium represents the balance

-   Silver powder has flake shape with a D50 particle size of 3.7 μm-   The % light reflection the above metallization after co-firing with    LTCC chip carrier at red (650 nm), green (510 nm), or blue (475 nm)    light wavelength is, respectively, 95.2%, 91.9% or 90.4% when silver    was fired upward, and 95.5%, 92.4%, or 90.9% when silver was fired    downward (i.e. facing the setter).

Example 26

Silver Inner Signal Conductor Silver Powder 77.0Ethyl cellulose/texanol-based medium represents the balance

-   Silver powder has irregular shape with a D50 particle size of 8.2 μm-   The % light reflection the above metallization after co-firing with    LTCC chip carrier at red (650 nm), green (510 nm), or blue (475 nm)    light wavelength is, respectively, 98.7%, 97.7% or 97.0%.

Example 27

Silver Inner Signal Conductor Silver Powder 77.0 Frit #17 0.5Ethyl cellulose/texanol-based medium represents the balance

-   Silver powder has irregular shape with a D50 particle size of 8.2 μm-   The % light reflection the above metallization after co-firing with    LTCC chip carrier at red (650 nm), green (510 nm), or blue (475 nm)    light wavelength is, respectively, 95.7%, 93.0% or 91.9% when silver    was fired upward, and 94.8%, 91.3%, or 89.7% when silver was fired    downward (i.e. facing the setter).

Example 28

Silver Inner Signal Conductor Silver Powder 77.0Ethyl cellulose/texanol-based medium represents the balance

-   Silver powder has flake shape with a D50 particle size of 6.0 μm-   The % light reflection the above metallization after co-firing with    LTCC chip carrier at red (650 nm), green (510 nm), or blue (475 nm)    light wavelength is, respectively, 98.8%, 97.7% or 97.0%.

Example 29

Silver Inner Signal Conductor Silver Powder 77.0 Frit #17 0.5Ethyl cellulose/texanol-based medium represents the balance

-   Silver powder has flake shape with a D50 particle size of 6.0 μm-   The % light reflection the above metallization after co-firing with    LTCC chip carrier at red (650 nm), green (510 nm), or blue (475 nm)    light wavelength is, respectively, 94.0%, 90.3% or 88.6% when silver    was fired upward, and 94.9%, 91.5%, or 89.9% when silver was fired    downward (i.e. facing the setter).

Example 30

Silver external wire bondable Conductor Silver Powder 83.4 PlatinumPowder 0.4 Metallic Oxides 0.4 Bismuth Trioxide 0.5Ethyl cellulose/texanol-based medium represents the balance

-   Silver powder has flake shape with a D50 particle size of 2.0 μm-   The % light reflection the above metallization after co-firing with    LTCC chip carrier at red (650 nm), green (510 nm), or blue (475 nm)    light wavelength is, respectively, 92.8%, 89.1 % or 87.9% when    silver was fired upward, and 92.4%, 88.3%, or 86.4% when silver was    fired downward (i.e. facing the setter).

Table 3 compares the TCE and thermal conductivity of the above heat sinkmaterials.

TABLE 3 Joining Materials TCE, 10E-6/C Thermal Conductivity Cu—W 5-10200 W/mK Cu—Mo 5-10 200 W/mK Cu—Mo—Cu 5-10 200 W/mK Al—SiC 3-15 150 W/mKBeO 5-7  260 W/mK AlM 4-5  200 W/mK

1. A thick film dielectric tape composition for use in lightingapplications comprising, in weight percent total tape composition: (a)40 to 70 weight percent glass frit; (b) 30 to 60 weight percentrefractory ceramic filler; (c) 0 to 10 weight percent of one or moreinorganic pigments; dispersed in (d) organic medium, wherein saidrefractory ceramic filler and said inorganic pigment have a refractoryindex in the range of 1.5 to 3.5 and said refractory ceramic filler hasa flexural strength of at least 150 Mpa.
 2. The composition of claim 1wherein said refractory ceramic filler is alumina.
 3. The composition ofclaim 1 wherein said inorganic pigment is selected from titanium oxide,zinc sulfite, calcium fluoantimonate, zirconium oxide, lead arsenate,antimony trioxide, tin oxide, zirconium silicate, zinc spinel, aluminumoxide, and mixtures thereof.
 4. The composition of claim 1 wherein saidglass frit is a lead-containing glass comprising in weight percent,based on total composition: SiO₂ 55-58, Al₂O₃ 8-10, PbO 16-18, B₂O₃3.5-5.5, CaO 7-9, MgO 0.4-0.8, Na₂O 2.1-2.7, K₂O 1.2-2.2.
 5. Thecomposition of claim 1 wherein said glass frit is a lead-free glasscomprising in weight percent, based on total composition: SiO₂ 52-55,Al₂O₃ 11.0-14.5, B₂O₃ 8-9, CaO 15-18, MgO 0.5-3, Na₂O 1.5-3.0, Li₂O0.2-0.6, K₂O 1-3, SrO 1-4.5.
 6. A light emitting diode module having twoor more LTCC (low temperature co-fired ceramic) tape layers; each tapelayer comprising 40 to 70 weight percent glass frit; 30 to 60 weightpercent refractory ceramic filler; 0 to 10 weight percent of one or moreinorganic pigments; dispersed in organic medium, wherein said refractoryceramic filler and said inorganic pigment have a refractive index in therange of 1.5 to 3.5 and said refractory ceramic filler has a flexuralstrength of at least 150 MPa; having one or more cavities in said tapelayers; having at least two electrical vias and at least one thermal viain said tape layers; having at least one functioning light emittingdiode chip; wherein said LTCC (low temperature co-fired ceramic) tapelayers provide a desired circuit pattern and said circuit pattern iselectrically connected through said electrical vias, thus, forming afunctioning chip carrier and wherein at least one functioning lightemitting diode chip is mounted to said chip carrier and wherein at leastone thermal via is connected to a heat sink and wherein said thermal viadissipates heat released from said functioning light emitting diode chipthrough its connection to said heat sink; wherein said module is used ina light emitting diode application selected from high brightness lightemitting diode device, liquid crystal display, display-related lightsources, automotive lighting, decorative lighting, signage andadvertisement lighting, liquid crystal display device as a backlightunit, and information display applications.
 7. A light emitting diodemodule having two or more LTCC (low temperature co-fired ceramic) tapelayers; each tape layer comprising 40 to 70 weight percent glass frit;30 to 60 weight percent refractory ceramic filler; 0 to 10 weightpercent of one or more inorganic pigments; dispersed in organic medium,wherein said refractory ceramic filler and said inorganic pigment have arefractive index in the range of 1.5 to 3.5 and said refractory ceramicfiller has a flexural strength of at least 150 MPa; having one or morecavities in said tape layers; having at least two electrical vias and atleast one thermal via in said tape layers; having at least onefunctioning light emitting diode chip; wherein said LTCC (lowtemperature co-fired ceramic) tape layers provide a desired circuitpattern and said circuit pattern is electrically connected through saidelectrical vias, thus, forming a functioning chip carrier and wherein atleast one functioning light emitting diode chip is mounted to said chipcarrier and wherein at least one thermal via is connected to a heat sinkand wherein said thermal via dissipates heat released from saidfunctioning light emitting diode chip through its connection to saidheat sink; wherein at least three functioning light emitting diode chipsare mounted to said chip carrier and wherein the color of saidfunctioning light emitting diode chips is selected from white, red,green, and blue.
 8. The light emitting diode module of claim 7 whereinsaid functioning light emitting diode chips have an operating wattage ofequal to or greater than 0.5 watts.
 9. The light emitting diode moduleof claim 7 wherein said functioning light emitting diode chips have anoperating wattage of equal to or greater than 1.0 watts.